KEYWORDS: Visualization, Color centers, Color difference, Data centers, Projection systems, Color reproduction, Solids, Image quality, Image quality standards, Colorimetry
The issue of accurate color reproduction is a hot topic, which is closely linked to the problem of accurate measurement
of the human visual threshold, or "Just Noticeable Difference" (JND). Since most imaging scientists believe that JND
experiments are too complicated and costly, "Visual Difference" (dV) experiments have gained high popularity.
Typically the results of dV experiments are extended in place of JND, and many scientists interchange dV for JND. For
example, the current standard color difference formula CIE DE 2000 was constructed on a dataset from dV experiments.
However, in order for the "dV to JND" transition to be correct, several assumptions are taken, and whose haven't
actually been proven. This paper proposes a relatively inexpensive experiment that will allow a precise JND
measurement experiment, which in turn will let verify the assumptions for the dV to JND transition, and perhaps offer a
better dataset for development of a more robust and solid color difference formula.
The paper presents an undertaking to develop most compact high dynamic range image compression format and shows that chromatic color coordinate system plays a central role in such development. Important design considerations, such as conditions and criterions of data accuracy, efficiency and characteristics of color space, are addressed along the way. An additional trade-off between data precision and data size is discussed, and new feature of parameterized precision is introduced. Detailed comparison of Bef, Luv, Yxy chromatic coordinates is performed and special case of color space singularities is analyzed. LinLogBef imaging format implementation is presented and compared against OpenEXR and Radiance HDR formats by compression ratio, relative error and dynamic range characteristics. Other benefits provided by LinLogBef are further discussed, such as the format's convenience for image editing operations.
KEYWORDS: Image processing, Colorimetry, High dynamic range imaging, Control systems, Photography, RGB color model, Algorithm development, Image quality, Spherical lenses, Digital photography
Any color image editing software has Brightness, Contrast, and Saturation controls. However, because it usually imitates
corresponding adjusting knobs of a Color TV, and thus, corresponds to mid 20th century scope of engineering, adjusting
one of the parameters affects all three parameters, and modification of Brightness or Contrast does not preserve
chromatic coordinates. A person should be very experienced with the sequential control operations in order to get a
result equivalent to a simple expocorrection.
A set of new generation algorithms described in this paper is free from the above-mentioned defects and includes:
Brightness and Contrast editing which does not affect chromatic coordinates; Local Contrast editing that causes only
minor modification of Global Dynamic Range; Global Dynamic Range modification which affects neither chromatic
coordinates, nor Local Dynamic Range; and Saturation modification which affects neither Brightness, nor Hue.
The efficiency of color image editing software depends on the choice of a basic CCS (Color Coordinate System). A CCS
that is effective for one editing procedure might be less effective for another. This paper presents a set of correlated
CCSs with a specification of their preferable area of application.
The main quality requirements for a digital still camera are color capturing accuracy, low noise level, and quantum
efficiency. Different consumers assign different priorities to the listed parameters, and camera designers need clearly
formulated methods for their evaluation. While there are procedures providing noise level and quantum efficiency
estimation, there are no effective means for color capturing accuracy estimation. Introduced in this paper criterion allows
to fill this gap.
Luther-Ives condition for correct color reproduction system became known in the beginning of the last century.
However, since no detector system satisfies Luther-Ives condition, there are always stimuli that are distinctly different
for an observer, but which detectors are unable to distinguish. To estimate conformity of a detector set with Luther-Ives
condition and calculate a measure of discrepancy, an angle between detector sensor sensitivity and Cohen's Fundamental
Color Space may be used.
In this paper, the divergence angle is calculated for some typical CCD sensors and a demonstration provided on how this
angle might be reduced with a corrective filter. In addition, it is shown that with a specific corrective filter Foveon
sensors turn into a detector system with a good Luther-Ives condition compliance.
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